In order to use solar energy effectively, solar power generation systems have been spreading wherein a large number of solar cell panels are arranged. About the solar power generation systems, various systems exist which range from small-scale systems each set on a house roof to large-scale systems each having a power generation quantity of 1 megawatt or more that can supply the regional electricity.
As illustrated in, for example, FIG. 1, in a large-scale system, plural solar cell modules 1 are connected to each other in series so as to constitute each solar cell string 2 and, if necessary, to an electric power end thereof is connected a diode 4 for backflow prevention. Both ends of the solar cell string 2 are connected to electric power cables 3 in order to collect electric power. The solar cell strings 2, which each have such a structure, exist in a large number. Electric powers generated in the individual strings are collected through the electric power cables 3, so as to be sent to a single collected-power terminal device. The collected power is to be an output of the solar power generation system.
In any solar power generation system, the power generation quantity of its solar cell modules or solar cell strings may lower due to an error in a work for setting up the system, a defect of parts thereof, a deterioration with age based on use over many years, a failure caused by thunder or the like, or an external factor such as weather, a maintenance thereof or a shadow. When the lowering of the power generation quantity is caused by any temporary external factor, the lowering may be ignored. However, when it is caused by a failure, it is desired to repair or exchange the corresponding module(s) or string(s) as soon as possible.
However, in a power generation system composed of many solar cell modules or solar cell strings, considerable time and labor are required for finding out only the module or string having failure by excluding the influence of external factor. It is difficult to know the existence of a failure itself, in particular, in a mega solar system as illustrated in FIG. 2, wherein one thousand or more strings or several thousands or more of modules are arranged in a site wider than an area several hundreds of meters square to give a power generation quantity of 1 megawatt or more. It is more difficult to locate the position of the failure.
A conventional detection of an abnormality of a solar power generation system is generally attained by taking each solar cell module which constitutes a solar cell panel as a unit, or by taking each solar cell string which is composed of plural solar cell modules as a unit.
For example, Patent Document 1 suggests solar cell modules each having detecting means for detecting an electric current or voltage by taking each solar cell module as a unit, and communicating means for making a communication in accordance with outputs from the plural detecting means. The aim of the above solar cell modules is to remove a necessity that a failure should be checked near each of the modules by a checking worker. However, only an abnormality of an electric parameter value can be detected. Thus, it is difficult to extract precisely only the solar cell module having failure by excluding the influence of external factor such as weather.
Patent Document 2 suggests an abnormality-detecting device for a solar cell wherein it is decided whether or not an abnormality is generated in the solar cell by making a comparison between a calculated power generation quantity data of the solar cell over a given period and a power generation quantity data which was measured in a situation corresponding to the situation that the above calculated power generation quantity data was measured and which has been already memorized in memorizing means. This device is a device wherein a comparison is made between power generation quantity data measured at times similar to each other in weather, so as to make a decision, thereby decreasing the influence of changes in the situation of the surroundings, such as a weather-dependent change in solar radiation quantity. However, it is difficult to appropriately extract, from power generation quantity data in the past, a similar comparative data. Additionally, there remains a problem that the precision of the decision becomes very low when an unpredicted change in weather is caused over a day. Furthermore, it is a very troublesome work to memorize power generation quantity data in the past and process the data so as to be usable, as data for comparison, in accordance with weather or seasons. As a result, a problem that the work makes the system complicated is caused.
Patent Document 3 suggests a solar power generation system wherein when a change has been made in a quantity more than a predetermined quantity between past power generation data and the present power generation data, a statement that the change has been made is displayed. This system also compares the present power generation data with power generation data in the past, and has the same problems as in Patent Document 2.